Transistor microphone



W. P. MASON TRANSISTOR MICROPHONE Oct. 11, 1966 Filed June 12, 1965lNl/E/VTOR W. F. MASON AT TORNEV United States Patent 3,278,696TRANSISTOR MICROPHONE Warren P. Mason, West Orange, N.J., assignor toBell Telephone Laboratories, Incorporated, New York, N.Y., a corporationof New York Filed June 12, 1963, Ser. No. 287,279 3 Claims. (Cl.179-110) This invention relates to electroacoustic and electromechanicaltransducers. More particularly, it relates to electroacoustic andelectromechanical transducers employing transistors.

In the copending joint application of P. Andreatch, Jr., and M. E.Sikorshi (Case 3-3), Ser. No. 216,456, filed Aug. 13, 1962, it isdisclosed that a transistor will respond as an electromechanicaltransducer to linearly directed stress applied normally to a point onthe emitter region which is independent of the electrical connect-ingfacilities to the emitter region.

In the copending sole application of M. E. Sikorski (Case 7), Se-r. No.282,792, filed May 23, 1963, it is further disclosed that a transistoris much more sensitive to stress applied normally to the emitter regionit the point of application of the stress is in close proximity to theedge of the emitter region. The above-mentioned sole application alsodiscloses that a statically prestressed transistor may be even moresensitive to superimposed variable stresses and may have a more linearresponse to such stresses where the amount of prestressing is adjustedto cause the transistor to be operating in a range of maximumsensitivity and linearity.

The present invention makes use of the above-mentioned disclosures byplacing the stress supplying indenter or needle on a point closelyadjacent to the edge of the emitter region of the transistor. In thecase of a transistor having a rectangul-arly shaped emitter region, thepoint is preferably at -a corner of the emitter region in closeproximity to both edges forming the corner.

The indenter applies a normally directed prestress as taught in theabove-mentioned sole application, and, in addition, applies thevibratory signal energy laterally to the indenter near its point ofcontact with the emitter region in a direction such that the point ofthe indenter tends to move alternately toward and away from theproximate edges of the emitter region. The result is an appreciablyenhanced sensitivity of the transducer to stress as compared with anyknown prior art transducer Including the above-mentioned transducers ofSikorski and Andreatch.

In acco-rdancewith a further teaching of the present invention, the useof a tripod of three indenters to apply stress to three spaced pointsnear the edges of the emitter region is taught. The use of threeindenters provides an arrangement which is mechanically much more stablethan one employing a single indenter only. A correspondingly increasedportion of the emitter periphery can also be subjected to the signalvibrations. Furthermore, the total normal force may be divided betweenthe three indenters thereby reducing the force on each indenter.

Accordingly, a principal object of the invention is to increase thesensitivity of transducers which employ the stress responsivecharacteristics of transistors.

Another object is to increase the mechanical stability of devices of theinvention.

Other and further objects, features and advantages of the invention willbecome apparent from a perusal of the following detailed description ofillustrative structural arrangements embodying the principles of theinvention taken in conjunction with the acompanying drawing, in which:

FIG. 1 illustrates a structure of the invention employing a singleindenter; and

FIG. 2 illustrates a structure of the invention employing threeindenters.

In more detail in FIG. 1, a transistor is shown which comprises acollector portion 1, a base portion 2 and an emitter portion 3, thelast-named portion being induced in the base portion 2, for example, bydiffusion of appropriate impurities, all substantially as illustratedand described in the above-mentioned copending joint and soleapplications of M. E. Sikorski. Electrical connections are made, to theemitter portion by lead 9 connecting to metallized terminal strip 8, tothe base portion by leads 6 and 7 connecting to metallized terminalstrips 4 and 5, respectively, on the base portion, and to the collectorportion by lead 10 making an ohmic connection thereto. Appropriateelectrical circuits for association with the transistor are illustratedand described in the above-mentioned sole application of M. E.Sik-orski. Other appropriate circuits of numerous varieties are wellknown and extensively used by those skilled in the art.

The over-all structural arrangement of FIG. 1 differs from any knownprior art in that the vibratory signal energy illustrated as beingderived from acoustic waves represented by arrows 42 impinging ondiaphragm 36 is impressed transversely on the indenter 11 via link rod32, as shown. Diaphragm 36 is held by a rigid rim 3-8, the latter beingheld by base 40 resting on a fixed support 22.

Assuming that the point of contact P of indenter 11 with the emitterregion 3 is at a corner of the upper surface of the emitter region, thedirection of the vibratory energy transmitted through link rod 32 isalong line 20, bisecting the right angle formed by the corner.

A small vertical pressure is exerted longitudinally along indenter 11 byan adjustable spring arrangement comprising a housing cylinder 24,supported by a fixed support 22, housing 24 enclosing spring 26 betweenthe upper piston 25 and lower piston 28, the latter including a hingedconnection to indenter 11 which permits transverse motion of the lowerend of indenter 11 along the line 20 previously mentioned. The upperpiston 25 is supported on threaded rod 23 which projects through anappropriately threaded hole in the upper surface of housing 24 so thatthe force exerted by spring 26 on indenter 11 can be readily adjustedfor optimum performance. As stated in Sikorskis above-mentionedcopending sole application, with indenter 11 pressing on a point P atthe corner of the emitter region only a slight prest-ress is required toinsure maximum sensitivity and linearity.

When rod 32 is exerting a force directed along line 20 toward the morecentral portion of the emitter region the response of the transistor isappreciably decreased and when rod 32 is exerting a force in theopposite direction, that is, toward the adjacent edges of the emitterregion, the response of the transistor is appreciably augmented. Thusthe overall structure of FIG. 1 constitutes a highly sensitivetransistor microphone. Alternatively, link bar 32 can obviously transmitvibratory mechanical energy from a phonograph pickup device or the like.

It should be borne in mind that transistors are normally of very smalldimensions and for adequately illustrative drawings it is necessary toshow them to a greatly enlarged scale.

The arrangement of FIG. 2 can be similar to that of FIG. 1,correspondingly numbered details being identical, except that theemitter region 54 having a metallized terminal 56 thereon includes asmall tab or projection 55, and metallized terminal 60 on base region 52is notched to partially enclose tab 55, as shown. Also, three indenters70, 72 and 74 on triangular plate 76 are carried in a tripod arrangementon rod 78 and make contact with points Q, R and S, respectively, asindicated in the drawing. The base region 52 has a second metallizedterminal region 58 on the other side of the emitter region 54.

Electrical connections to the three regions 50, 5-2 and 54,respectively, of the transistor can be made as for the structure ofFIG. 1. In FIG. 2 link rod 32 transmits its transverse vibratory energyin the direct-ion of the horizontal center line of tab 55, to supportingrod 78, so that all three indenters are simultaneously impelledalternately toward and away from the proximate portions of the edges ofthe emitter region.

The arrangement of FIG. 2 oflFers in the tripod arrangement of indentersa mechanically more stable arrangement effective over an increasedportion of the emitter edge. Furthermore, the total vertical force orprestress can be divided between the three indenters.

Numerous and varied modifications and rearrangements of theabove-described illustrative embodiments can readily be devised by thoseskilled in the art without departing from the spirit and scope of theprinciples of the invention.

What is clamied is:

1. An electromechanical transducer comprising a transistor having athree-dimensional emitter region, a threedimensional base region, a p-njunction between said emitter and base regions enveloping all but anouter surface of said emitter region, an inden'ter impinging nonmallyupon the outer-surface of the emitter region at a point closely adjacentan edge of the outer surface of said emitter region, means for exertinga specific static force longitudinally through the indenter at saidpoint, and means for exerting a vibratory mechanical sign-a1 upon saidindenter transverse-1y to said inden-ter and to the adjacent edge ofsaid emitter region.

2. The arrangement of claim 1 in which the static force is of anamplitude to pres'tress the emitter region to an operating point of itsstress-responsive characteristic at which substantially maximumsensitivity and linearity are obtained.

3. The arrangement of claim 1 in which a tripod arr-angement of threeindenters is employed, the specific static force being divided equallybetween the three indenters.

No references cited.

KATHLEEN H. CLAFFY, Primary Examiner. I

F. N. CARTEN, Assistant Examiner.

1. AN ELECTROMECHANICAL TRANSDUCER COMPRISING A TRANSISTOR HAVING ATHREE-DIMENSIONAL EMITTER REGION, A THREEDIMENSIONAL BASE REGION, A P-NJUNCTION BETWEEN SAID EMITTER AND BASE REGIONS ENVELOPING ALL BUT ANOUTER SURFACE OF SAID EMITTER REGION, AN INDENTER IMPINGING NORMALLYUPON THE OUTER SURFACE OF THE EMITTER REGION AT A POINT CLOSELY ADJACENTAN EDGE OF THE OUTER SURFACE OF SAID EMITTER REGION, MEANS FOR EXERTINGA SPECIFIC STATIC FORCE LONGITUDINALLY THROUGH THE INDENTER AT SAIDPOINT, AND MEANS FOR EXERTING A VIBRATORY MECHANICAL SIGNAL